The Troehites were recognized as simply the
broken portions of the stem of some of these old fossil Crinoids, and
the Crinoids themselves were seen to be the ancient representatives of
the present Comatulae and Star-Fishes with stems. So is it often with
the study of Nature; many scattered links are collected before the man
comes who sees the connection between them and speaks the word that
reconstructs the broken chain.
I will begin my comparison of all Echinoderms with an analysis of the
Star-Fishes and Sea-Urchins, because I think I can best show the
identity of parts between them, notwithstanding the difference in
their external form; the Sea-Urchins having always a spherical body,
while the Star-Fishes are always star-shaped, though in some the star
is only hinted at, sketched out, as it were, in a simply pentagonal
outline, while in others the indentations between the rays are very
deep, and the rays themselves so intricate in their ramifications as to
be broken up into a complete net-work of branches. But under all this
variety of outline, our problem remains always the same: to build with
the same number of pieces a star and a sphere, having the liberty,
however, of cutting the pieces differently and changing their relative
proportions.
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